<template>
    <div class="pagination">
      <button :disabled="pageNo==1" @click="$emit('getPageNo', pageNo-1)">上一页</button>  
      <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo', 1)" :class="{active:pageNo==1}">1</button>
      <button v-if="startNumAndEndNum.start > 2">···</button>
  
      <button v-for="(page, index) in startNumAndEndNum.end" :key="index" v-if="page >= startNumAndEndNum.start" @click="$emit('getPageNo', page)" :class="{active:pageNo==page}">{{ page }}</button>
      
      <button v-if="startNumAndEndNum.end < totalPage - 1">···</button>
      <button v-if="startNumAndEndNum.end < totalPage" @click="$emit('getPageNo', totalPage)" :class="{active:pageNo==totalPage}">{{totalPage}}</button>
      <button :disabled="pageNo == totalPage" @click="$emit('getPageNo', pageNo+1)" >下一页</button>
      
      <button style="margin-left: 30px">共 {{ total }} 条</button>
    </div>
  </template>
  
  <script>
    export default {
      name: "Pagination",
      props:["pageNo","pageSize","total","continues"],
      //计算属性
      computed:{
        //总共多少页
        totalPage() {
          //向上取整
          return Math.ceil(this.total / this.pageSize);
        },
        //计算出连续页码的起始数字与结束数字[连续页码数字至少是5]
        startNumAndEndNum() {
            //解构出连续的页码数、当前页码、总页数
            const {continues, pageNo, totalPage} = this;
            //先定义两个变量存储起始数字与结束数字
            let start = 0 , end = 0;
            //连续页码数字5【就是至少5页】，如果出现不正常现象
            //不正常现象：总页数没有连续页码多
            if(continues > totalPage) {
                start = 1;
                end = totalPage;
            }else{
              //正常现象【连续页码5，但是总页数一定是大于5的】
              //起始数字
              start = pageNo - parseInt(continues / 2);
              //结束数字
              end = pageNo + parseInt(continues / 2);
              //把出现不正常的现象【start数字出现0|负数】纠正
              if(start < 1) {
                start = 1;
                end = continues;
              }
              //把出现不正常的现象【end数字大于总页码】纠正
              if(end > totalPage) {
                end = totalPage;
                start = totalPage - continues + 1;
              }
            }
            return {start, end};
        }
      }
    }
  </script>
  
  <style lang="less" scoped>
    .pagination {
      text-align: center;
      button {
        margin: 0 5px;
        background-color: #f4f4f5;
        color: #606266;
        outline: none;
        border-radius: 2px;
        padding: 0 4px;
        vertical-align: top;
        display: inline-block;
        font-size: 13px;
        min-width: 35.5px;
        height: 28px;
        line-height: 28px;
        cursor: pointer;
        box-sizing: border-box;
        text-align: center;
        border: 0;
  
        &[disabled] {
          color: #c0c4cc;
          cursor: not-allowed;
        }
  
        &.active {
          cursor: not-allowed;
          background-color: #409eff;
          color: #fff;
        }
      }
    }
    .active{
      background: skyblue;
    }
  </style>